Display the Operator properties of an Active Add Primitive operator
You can display them, but i think you will get convoluted code.

def draw(self, context):

    # ... earlier stuff.

    operators = bpy.data.window_managers["WinMan"].operators    
    if operators and operators[-1].name == 'Add UV Sphere':
        this_op = operators[-1]
        col = layout.column()
        col.prop(this_op.properties, 'segments')


But you'll notice you can drag the slider, it will update the visible value but not update the actual value of the active operator.



Then dynamically populating the UI with properties: 

 &gt;&gt;&gt; bpy.data.window_managers["WinMan"].operators[-1].properties.items()
 ...[('size', 2.0), ('view_align', 0), ('enter_editmode', 0), ('layers', &lt;bpy id property array [20]&gt;), ('location', &lt;bpy id property array [3]&gt;), ('segments', 9)]


so..

def draw(self, context):
    obj = context.active_object
    mode_string = context.mode
    edit_object = context.edit_object

    layout = self.layout
    col = layout.column()
    col.label(text="Generate objects:")

    if mode_string == 'OBJECT':
        layout.menu("INFO_MT_add", text="Add")
    elif mode_string == 'EDIT_MESH':
        layout.menu("INFO_MT_mesh_add", text="Add")

    operators = bpy.data.window_managers["WinMan"].operators    
    if operators and operators[-1].name == 'Add UV Sphere':
        this_op = operators[-1]
        col = layout.column()
        for k, v in this_op.properties.items():
            col.prop(this_op.properties, k)


Would produce this, by inspecting the items in the properties of the current operator.



But, there are fundamental problems with this. You would have to limit somehow the kind of Operators to show in this list. Right now i've limited to Add UV Sphere, if you don't do that it will show all most recent Operator properties even if they aren't a Primitive operator..

So you might construct a set of Operator names to allow.. 

showable = {'Add UV Sphere', 'Add Cube', ....... }
if operators and operators[-1].name in showable:
   # ... display them as shown above


And still you won't be able to tweak these props. :( 

Seen as the operator has a perfectly good Operator Properties panel accessible from F6, and the panel also appears in the 'TOOLS' shelf, I'm inclined to discourage trying to do this. -- But it's an interesting thought experiment.